Vibration - has me stumped

stevick · Post by **stevick** » 26 Oct 2009, 21:24

I need help from you great diagnosticians. Here's the symptoms/history:
- I'm getting a curious vibration from the front end or engine. It is very noticeable when driving 40-60+mph over dips in the road or accelerating through a lefthand curve, giving the effect that you are driving over a washboard at the bottom of the dip or in the curve. It only occurs when under very slight to moderate acceleration and disappears entirely when you let off the gas or accelerate hard. You can coast through a dip or L curve without any vibration. It is significantly worse when there is a passenger in the car, making the vibration more constant (not limited to dips/L curves).
- 2000 S80 2.9 with 284k miles - the only DTCs are ECM 644A (cam reset valve) and CCM 001B & 001C (lower climate control switches - headrest release, STC, and truck valet switches are inoperative). Idle is fine and tranny shifts okay. Also had ECM 6440, but it cleared when I replaced the cam reset valve with a used one - ECM 644A remains though. I haven't checked for a slipped tooth on the timing belt yet and can only pray it's not the VVT unit. Oil is good, with no sludge in the oil passages. The car has sport springs (~1" lower), new rear shocks, and 2 year old struts/mounts/bearings. Condition of the motor mounts is unknown, but I'm on the third upper torque mount in as many years and the current one is going. Only other known issue with the car is a split inner CV boot on the front right axle, and I've noticed a click when pulling out on a left turn.

Could the VVT problem be causing the vibration? If so, why would suspension loading affect the vibration? If it's a suspension/alignment related problem, why would it appear/disappear based entirely on throttle position without change in forward speed? Where should I be looking? Any suggestions would be greatly appreciated, particularly if does not involve a dealer, as the local dealer closed (good riddance) and I probably couldn't afford them anyway.

Post by **vegasjetskier** » 26 Oct 2009, 21:33

My guess is CV joint.

volvo_boy_88 · Post by **volvo_boy_88** » 26 Oct 2009, 23:31

You know, this sounds similar to a problem I was having. I dont know if its the same, but it sounds similar. I didnt have any vibration going over bumps or anything, but I do remember whenever I made a L turnaround I would hear a clicking sound. I found out that my front axles are cracked so the axles might need replacing, but yours sounds a little different. But I just thought I would share that with you.

Post by **polskamafia mjl** » 27 Oct 2009, 00:08

It does indeed sound like a CV joint.

stevick · Post by **stevick** » 28 Oct 2009, 15:23

Thanks guys, looks like the CV joint is the consensus. I just ordered a rebuilt axle and will install this weekend (many thanks to the forum for a great how-to post).

While we're at it, any thoughts on the VVT problem?

Post by **vegasjetskier** » 28 Oct 2009, 16:00

stevick wrote:While we're at it, any thoughts on the VVT problem?

The valve (assuming that's the problem) is pretty easy to replace. It costs about $150, IIRC. You remove the spark plug cover, disconnect the wires, take out a couple bolts, and the valve comes right off. It's on the timing belt end of the head.

stevick · Post by **stevick** » 29 Oct 2009, 06:43

VJ - I have already replaced the original with a used one. I still have the ECM 644A. Is it likely the replacement is bad too? The cost of replacing with a rebuilt unit is not too bad, but I hate spending it if that's not the cure and there would be even more spending to come.

Post by **RobTheModd** » 29 Oct 2009, 07:41

volvo_boy_88 wrote:You know, this sounds similar to a problem I was having. I dont know if its the same, but it sounds similar. I didnt have any vibration going over bumps or anything, but I do remember whenever I made a L turnaround I would hear a clicking sound. I found out that my front axles are cracked so the axles might need replacing, but yours sounds a little different. But I just thought I would share that with you.

That is spot on. My 850 was making clicking sounds on the front right, turned out i had a bad cv joint. was cheaper to replace the whole axle.

stevick · Post by **stevick** » 02 Nov 2009, 19:16

Installed the new axle over the weekend. The how-to post was fantastic. The result was fantastic too, as the CV joint was clearly the problem. Now the car rides like new again! Thanks to all who helped. On top of that, my long battle with the VVT problem seems to be over too, as a 200 mile trip last week seems to have resolved it. The cleared code has not returned. Now, if I could just figure out which of the lower climate switches is bad, and replace it, all would be perfect again.

stevick · Post by **stevick** » 03 Nov 2009, 16:45

Oops, spoke too soon, as the ECM-644A is back. Car runs great though and with the new axle it drives like a dream.